Since digital media such as video DVDs and audio CDs allow perfect reproduction of digital data stored on them, there is a need for sophisticated copy protection systems to prevent extensive piracy. Without any form of copy control, films, audio recordings, and other digital content distributed on DVD disk or CD-ROM can be easily recorded by a digital recorder onto a digital data storage medium such as a recordable DVD disk, from which they can be further copied numerous times onto other DVD disks, without any degradation in the copy quality.
To prevent unauthorized copying, devices sold to consumers incorporate copy protection mechanisms. For example, copy protection information can be embedded in the data sector of a DVD disk. A possible method of copy control using such embedded information is for the digital content provider to supply the film or other digital content on a read-only medium, for example a DVD-ROM disk, with a flag that prevents copying embedded in the data. The DVD player/recorder will check for the presence of this flag and, if an attempt is made to copy the disk when the flag is present, the recording circuitry will prevent recording. However, this type of protection can be circumvented by using DVD-ROM/RAM drives as peripherals for computers, so as to enable copying of the data from an original disk onto a recordable disk on a bit-by-bit basis, including the copy protection information.
To prevent such bypassing of the protection scheme, some DVD players are designed to check for the presence of “Do Not Copy” flags on recordable disks as opposed to ROM disks. The presence of such a flag on a recordable disk is taken to indicate that the disk is an unauthorized copy of an original ROM disk, so that playback of the data on the disk will be prevented. Otherwise, if the player detects that a ROM disk is being used, it will play back the data on the disk.
However, this scheme works on the premise that a computer user copying the disk will copy all of the data on a bit-by-bit basis, including the “Do Not Copy” flag. The scheme can still be easily bypassed by the computer user who knows or determines where the copy control information is located on an original ROM disk, and who can therefore change or overwrite this information when making a copy of the original disk onto a recordable disk.
A further problem with the above-described protection scheme is that it is inflexible, with no way of providing for a copy management system, which governs the extent to which copying is permitted. For example, there is no way of providing for the contents of an original data storage medium to be copied to a backup medium, while preventing the production of a further generation of copies from the backup medium.